Williams D.A.,Arizona State University |
Greeley R.,Arizona State University |
Manfredi L.,Arizona State University |
Fergason R.L.,Astrogeology Science Center |
And 8 more authors.
Earth and Planetary Science Letters | Year: 2010
We used Thermal Emission Spectrometer (TES), Thermal Emission Imaging System (THEMIS), High-Resolution Stereo Camera (HRSC), and Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) data to assess the physical and compositional properties of the Malea Planum portion of the Circum-Hellas Volcanic Province (CHVP). Our analysis of surface materials shows that the thermal inertia decreases from north to south, and that there is greater dust cover on the flanks of the CHVP volcanoes than in their putative calderas. Local variations in thermal inertia in Malea Planum are likely due to variations in surface material caused by aeolian and periglacial/permafrost processes, whereas regional variations are likely due to seasonal deposition and sublimation of ice at higher latitudes. Spectral analysis of OMEGA data indicates the widespread presence of pyroxenes and/or olivine, particularly in the rims of craters that likely excavated volcanic materials. Dark materials occur throughout the CHVP, but are concentrated in topographic lows such as crater and caldera floors. Derivation of modal mineralogies from OMEGA data show a variation in composition of dark materials across Malea Planum: eastern dark deposits have higher olivine and low-calcium pyroxene contents, lower high-calcium pyroxene contents, and higher ratios of low-calcium to total pyroxene, relative to western dark deposits. Correlation with cratering-model age estimates suggests that the western deposits are associated with older features (3.8. Ga) than the eastern deposits (3.6. Ga), but these age differences are within uncertainties. Nevertheless, these results suggest a potential change in composition of volcanic materials in the Malea Planum portion of the CHVP with space, and possibly time. © 2009 Elsevier B.V.
Tosi F.,National institute for astrophysics |
Orosei R.,National institute for astrophysics |
Seu R.,University of Rome La Sapienza |
Coradini A.,National institute for astrophysics |
And 21 more authors.
Icarus | Year: 2010
We apply a multivariate statistical method to Titan data acquired by different instruments onboard the Cassini spacecraft. We have searched through Cassini/VIMS hyperspectral cubes, selecting those data with convenient viewing geometry and that overlap with Cassini/RADAR scatterometry footprints with a comparable spatial resolution. We look for correlations between the infrared and microwave ranges the two instruments cover. Where found, the normalized backscatter cross-section obtained from the scatterometer measurement, corrected for incidence angle, and the calibrated antenna temperature measured along with the scatterometry echoes, are combined with the infrared reflectances, with estimated errors, to produce an aggregate data set, that we process using a multivariate classification method to identify homogeneous taxonomic units in the multivariate space of the samples.In medium resolution data (from 20 to 100. km/pixel), sampling relatively large portions of the satellite's surface, we find regional geophysical units matching both the major dark and bright features seen in the optical mosaic. Given the VIMS cubes and RADAR scatterometer passes considered in this work, the largest homogeneous type is associated with the dark equatorial basins, showing similar characteristics as each other on the basis of all the considered parameters.On the other hand, the major bright features seen in these data generally do not show the same characteristics as each other. Xanadu, the largest continental feature, is as bright as the other equatorial bright features, while showing the highest backscattering coefficient of the entire satellite. Tsegihi is very bright at 5 μm but it shows a low backscattering coefficient, so it could have a low roughness on a regional scale and/or a different composition. Another well-defined region, located southwest of Xanadu beyond the Tui Regio, seems to be detached from the surrounding terrains, being bright at 2.69, 2.78 and 5 μm but having a low radar brightness. In this way, other units can be found that show correlations or anti-correlations between the scatterometric response and the spectrophotometric behavior, not evident from the optical remote sensing data. © 2010 Elsevier Inc.
McCord T.B.,The Bear Fight Center |
Hansen G.B.,University of Washington |
Combe J.-P.,The Bear Fight Center |
Hayne P.,The Bear Fight Center |
Hayne P.,University of California at Los Angeles
Icarus | Year: 2010
The surface composition of Europa is of great importance for understanding both the internal evolution of Europa and its putative ocean. The Near Infrared Mapping Spectrometer (NIMS) investigation on Galileo observed Europa and the other Galilean satellites from 0.7 to 5.2μm with spatial resolution down to a few kilometers during flybys by the spacecraft as it orbited Jupiter. These data have been analyzed and results published over the life of the Galileo mission and afterward. One result was the discovery of hydrated minerals at some locations on Europa and Ganymede. The data are noisy, especially for Europa, due to radiation affecting the NIMS electronics and detectors, and other artifacts are also present. The NIMS data are now being reprocessed using the accumulated knowledge gained over the entire missions to remove noise spikes and compensate for some other defects in the data. We are analyzing these reprocessed data in an attempt to defined better the nature of the hydrate spectral features and improve their interpretation. We report here on analyses of two NIMS reprocessed observations for the 0.7-3-μm region. A revised hydrate spectrum is calculated and mapped in detail across two lineaments. The spectrum shows the expected distorted water features but little or no spectral structure in these features. A narrow, weak spectral feature appears at 1.344μm, which is weakly correlated with lower albedo. Several other weak features may be present but are difficult to confirm in these limited data sets. The hydrate signature shows the greatest strength within and toward the center of the lineaments, confirming and strengthening the association of the hydrate with these endogenic features. This trend may indicate that the material in the lineaments is youngest toward the center and has more water frost coverage toward the edge. A small, visually dark, circular feature has a spectrum that shows both hydrate and crystalline water ice features and perhaps contains a hydrate different in spectral characteristics and perhaps composition than found in the lineament. © 2010 Elsevier Inc.
Castillo-Rogez J.C.,Jet Propulsion Laboratory |
McCord T.B.,The Bear Fight Center
Icarus | Year: 2010
We model Ceres' thermo-physical-chemical evolution by considering a large range of initial conditions as well as various evolutionary scenarios. Models are constrained by available shape measurements, which point to a differentiated interior for Ceres. We address the role played by hydrothermal activity in the long-term evolution of Ceres and especially the evolution of its hydrosphere. We suggest that models with times of formation shorter than about 5 My after the production of calcium-aluminum inclusions are more likely to undergo hydrothermal activity in their early history, which affects Ceres' long-term thermal evolution. We evaluate the conditions for preserving liquid water inside Ceres, a possibility enhanced by its warm surface temperature and the enrichment of its hydrosphere in a variety of chemical species. However, thermal modeling of the hydrosphere needs to be further investigated. We show that shape data can help constrain the amount of hydrated silicate in the core, and thus the extent of hydrothermal activity in Ceres. We discuss the importance of these results for the Dawn mission's arrival at Ceres in 2015. © 2009 Elsevier Inc.